Transcription, Alternative Splicing, and Post-Translational Regulation of CaLOXs in the Dynamic Regulation of Jasmonate Levels in Wounded Pepper Leaves

In response to stresses, jasmonates increase rapidly, leading to plant resistance against necrotrophic pathogens and chewing insect herbivores. Jasmonate biosynthesis is regulated at many levels, including transcriptionally, through alternative splicing, and the phosphorylation of the 13<i>S</i>-lipoxygenase (LOX) that catalyzes an early step in jasmonate biosynthesis. In pepper, transcriptomic analysis of a foliar wounding time course was conducted to deepen our understanding of these regulatory mechanisms. All four <i>CaLOX</i>s are constitutively expressed. <b><i>CaLOX2</i></b>, which encodes an enzyme with a Ser in a predicted regulatory phosphosite, shows a rapid but short-lived increase in wound-induced expression. In contrast, <b><i>CaLOX7</i></b>, which encodes a protein with a non-phosphorylatable Ala at the phosphosite, shows higher wound-induced expression at 6 h. As well, at this timepoint, there is a predicted increase in exon 4 retention in <b><i>CaLOX8</i></b> transcripts in wounded plants. ChimeraX protein modeling predicts that the retention of exon 4 may negatively affect enzyme activity, possibly by blocking access to the enzyme's active site. The transcription, alternative splicing, and post-translational regulation of CaLOX enzymes support the dynamic fluctuations observed in the jasmonates, which increase rapidly upon wounding and return to basal levels at 6 h post-stress.